Biomass-derived carbon electrodes: Key parameters for understanding the electrocatalytic performance

The conversion of biomass into carbon materials has become an essential pillar of sustainability in electrochemical technologies. However, biomass-derived carbons and their electrodes are complex materials. This opinion article raises concerns about the need to correlate physicochemical properties of these carbon materials with those of the biomass precursor, the electrode composition and the electrode/electrolyte interface to rationalize the comprehension of their electrocatalytic performance. The electrocatalytic activity of biomass-derived carbons in aqueous environments is discussed for several reactions of interest in terms of the nature and stability of electroactive sites and the ability to form radicals. All these are strongly related to the characteristics of the carbon material (composition, type of functional groups, porosity, structural order) and the manufacture of those electrodes. Concerns are also raised about the ambiguities and misconceptions associated to the lack of consensual terminology on biomass-derived carbons. Finally, recommendations are presented when reporting the electrocatalytic activity of biomass-derived carbons; emphasis should be paid to demonstrate the reproducibility of biomass-derived carbon electrodes and their stability through long-term electrocatalytic assays.The authors thank the financial support of region Centre Val de Loire APR-IA program (CA, grants MOSAIK, MATHYFON) and NextGenerationEU (AG-B, grant ZAMBRANO21 10). TS and AF thank the CSC (fellowship 202006460009) and Univ. Orléans for their PhD fellowships

All-in-one continuous electrochemical monitoring of 2-phenylphenol removal from water by electro-Fenton treatment

The biggest allure of heterogeneous electro-Fenton (HEF) processes largely fails on its high efficiency for the degradation of a plethora of hazardous compounds present in water, but still challenging to search for good and cost-effective electrocatalyst. In this work, carbon black (CB) and oxidised carbon black (CBox) materials were investigated as cathodes in the electrochemical production of hydrogen peroxide involved in HEF reaction for the degradation of 2-phenylphenol (2PP) as a target pollutant. The electrodes were fabricated by employing carbon cloth as support, and the highest H2O2 production yields were obtained for the CBox, pointing out the beneficial effect of the hydrophilic character of the electrode and oxygen-type functionalization of the carbonaceous surface. HEF degradation of 2PP was explored at −0.7 V vs. Ag/AgCl exhibiting the best conversion rates and degradation grade (total organic carbon) for the CBox-based cathode. In addition, the incorporation of an electrochemical sensor of 2PP in line with the HEF reactor was accomplished by the use of screen-printed electrodes (SPE) in order to monitor the pollutant degradation. The electrochemical sensor performance was evaluated from the oxidation of 2PP in the presence of Fe2+ ions by using square wave voltammetry (SWV) technique. The best electrochemical sensor performance was based on SPE modified with Meldola Blue showing a high sensitivity, low detection limit (0.12 ppm) and wide linear range (0.5–21 ppm) with good reproducibility (RSD 2.3 %). The all-in-one electrochemical station has been successfully tested for the degradation and quantification of 2PP, obtaining good recoveries analysing spiked waters from different water matrices origins

Nanoporous carbon/WO3 anodes for an enhanced water photooxidation

This work provides new insights in the field of applied photoelectro chemistry based on the use of nanoporous carbons as additives to tungsten oxide for the photooxidation of water under potential bias. Using a nanoporous carbon of low surface functionalization as additive to WO3 we have shown the dependence of the photochemical oxidation of water with the wavelength of the irradiation source. Photoelectrochemical responses obtained under monochromatic illumination show a significant increase in the incident photon-to-current conversion efficiency (IPCE) values for electrodes featuring up to 20 wt% carbon additive. Photoelectrochemical transient responses also show a sharp potential dependence, suggesting that the performance of the electrodes is strongly influenced by the carrier mobility and recombination losses. Despite the modest IPCE values of the W/NC electrodes (due to high bulk recombination and poor electron transport properties of the electrodes), our data shows that the incorporation of an optimal amount of nanoporous carbon additive to WO3 can enhance the carrier mobility of the semiconductor, without promoting additional recombination pathways or shadowing of the photoactive oxide.COA thanks the financial support of the European Research Council through a Consolidator Grant (ERC-CoG-648161-PHOROSOL) and the Spanish MINECO (grants CTM2014/56770-R, CTQ2013-48280-C3-3-R). VC and DJF kindly thank the UK Catalysis Hub for resources and support provided via the membership of the UK Catalysis Hub Consortium and funded by EPSRC (grants EP/K014706/1, EP/K014668/1, EP/K014854/1, EP/K014714/1 and EP/M013219/1). AGB thanks her PhD fellowship (BES-2012-060410) and VC thanks the UK National Academy and the Royal Society by the support though the Newton International Fellows program

Photochemistry of nanoporous carbons: Perspectives in energy conversion and environmental remediation

The interest in the use of nanoporous carbon materials in applications related to energy conversion and storage, either as catalysts or additives, has grown over recent decades in various disciplines. Since the early studies reporting the benefits of the use of nanoporous carbons as inert supports of semiconductors and as electron acceptors that enhance the splitting of the photogenerated excitons, many researchers have investigated the key role of carbon matrices coupled to all types of photoactive materials. More recently, our group has demonstrated the ability of semiconductor-free nanoporous carbons to convert the absorbed photons into chemical reactions (i.e. oxidation of pollutants, water splitting, reduction of surface groups) opening new opportunities beyond conventional applications in light energy conversion. The aim of this paper is to review the recent progress on the application of nanoporous carbons in photochemistry using varied illumination conditions (UV, simulated solar light) and covering their role as additives to semiconductors as well as their use as photocatalysts in various fields, describing the photochemical quantum yield of nanoporous carbons for different reactions, and discussing the mechanisms postulated for the carbon/light interactions in confined pore spaces.This work was partially funded by the Spanish MINECO (CTM2014/56770-R) and the European Council Research through a Consolidator Grant (ERC-CoG-648161-PHOROSOL).Peer reviewe

Effect of confinement of horse heart cytochrome c and formate dehydrogenase from Candida boidinii on mesoporous carbons on their catalytic activity

This study reports the immobilization of two biocatalysts (e.g., cytochrome c—Cyt c—and the non-metalloenzyme formate dehydrogenase from Candida boidinii–cbFDH) on a series of mesoporous carbons with controlled pore sizes. The catalytic activity of the nanoconfined proteins was correlated with the pore size distribution of the carbon materials used as supports. The electrochemical behaviour of nanoconfined Cyt c showed direct electron transfer electroactivity in pore sizes matching tightly the protein dimension. The pseudo-peroxidase activity towards H2O2 reduction was enhanced at pH 4.0, due to the protein conformational changes. For cbFDH, the reduction of CO2 towards formic acid was evaluated for the nanoconfined protein, in the presence of nicotinamide adenine dinucleotide (NADH). The carbons displayed different cbFDH uptake capacity, governed by the dimensions of the main mesopore cavities and their accessibility through narrow pore necks. The catalytic activity of nanoconfined cbFDH was largely improved, compared to its performance in free solution. Regardless of the carbon support used, the production of formic acid was higher upon immobilization with lower nominal cbFDH:NADH ratios.NHI. VM and JI thank MINICINN, Spain (projects CTQ2013-48280-C3-3-R and CTQ2016-76231-C2-2-R) for financial support. COA thanks the financial support of the European Research Council through a Consolidator Grant (PHOROSOL 684161)

Nanoporous carbons for the electrochemical reduction of CO2: Challenges to discriminate the roles of nanopore confinement and functionalization

The use of porous carbons in the electrochemical reduction of CO2 (CO2ER) has become an active research area. Despite good faradaic efficiencies and production rates, understanding their electrocatalytic activity is challenging owing to the complexity of the CO2-nanoporous carbon interactions. In this opinion review, we emphasize on the critical importance of discriminating the impacts of nanopore confinement and surface functionalization of porous carbons on the CO2ER. We have performed a rational analysis of recent literature addressing this topic, comparing electrocatalytic performance with knowledge about CO2-porous carbon affinity. Reported data have been re-discussed focusing on a complete characterization of the carbon electrodes to correlate physicochemical characteristics and the electrocatalytic activity. A perspective view is provided for future directions on the use of porous carbons in the CO2ER.The authors thank the financial support of NextGenerationEU (AG-B, grant ZAMBRANO21 10), the European Research Council (C.A. grant ERC-CoG 648161), region Centre Val de Loire APR-IA program (C.A. grant MATHYFON) and the Spanish Ministry of Science, Innovation and Universities (J.I., grant PID2019-108136RB-C32). ST thanks the Santiago Grisolía program (fellowship 2021 51136H0435)

Perspectives in the use of biochars as low-cost CO2 adsorbents

The recognized versatility of biochar in environmental remediation issues opened up an increasing interest in its applications in multidisciplinary areas of science and engineering. Possible biochar applications include carbon sequestration, soil fertility improvement, pollution remediation and agricultural by-product/waste recycling. A proper application in specific environmental areas requires a fulfilled biochar chemico-physical characterization and overall properties. Please click on the file below for full content of the abstract

One-pot electrodeposition of multilayered 3D PtNi/polymer nanocomposite. H2O2 determination in aerosol phase

In this work, 3D-structured nanocomposites were synthesized in one pot by electrochemical deposition of alternating layers of an azo type polymer (polyazure-A) with platinum and nickel nanoparticles. The hybrid PtNi/poly(AzA) film was electrochemically deposited on screen-printed carbon electrodes by layer-by-layer assembly as a function of the number of cyclic voltammograms for electrodeposition of the conducting polymer and the electrode potential applied for electro-reduction of the metal salts. The physicochemical characteristics of the resulting films were studied using electrochemical and microscopic techniques. The 3D molecular nanoarchitecture presents a hollow porous structure dependent on the electrode potential set for the electro-reduction of Pt and Ni nanoparticles. The electrochemical sensor was validated in terms of sensitivity, limit of detection, stability and repeatability, exhibiting a highly sensitive H2O2 detection, with LoD 68.5 nM (S/N = 3) at 0.05 V vs. Ag-SPCE for the electrode modified with 20 cycles for the conducting polymer electrodeposition and −2.0 V for metal ions reduction. The aim of this work also included the outcome of the electrochemical sensor after incorporating the room temperature ionic liquid 1‑butyl‑2,3-dimethylimidazolium tetrafluoroborate within the PtNi/poly(AzA) film, which notably improved the analytical parameters of the system, with LoD 14.5 nM at the same potential. Therefore, as proof of concept, the PtNi/poly(AzA) film-based electrode was explored towards the suitability of an electrochemical sensor for the determination of hydrogen peroxide in aerosol phase. The outstanding features of the PtNi/poly(AzA) film-based electrode modified with the aforementioned ionic liquid allowed for the continuous monitoring of H2O2 in an aerosol stream generated with an ultrasonic diffuser at the low applied potential of 0.05 V. In addition, monitoring H2O2 samples through a series of ON/OFF switches for over 3 h, the sensor provided a fast and reproducible response.Grants PID2019–106468RB-I00 and PID2019–108136RB-C32 funded by MCIN/AEI/10.13039/501100011033 and grant 2022‐GRIN‐34199 funded by the own research plan of the UCLM and co-financed by the European Fund for Regional Development (FEDER). RJP is the beneficiary of a postdoctoral contract associated with the first indicated project from the MCIN/AEI. This research was also partially funded by the Next-Generation EU funding (Zambrano21–10, AGB)

Ethanol dehydration via azeotropic distillation with gasoline fractions as entrainers: A pilot-scale study of the manufacture of an ethanol–hydrocarbon fuel blend

We establish experimentally and through simulations the economic and technical viability of dehydrating ethanol by means of azeotropic distillation, using a hydrocarbon as entrainer. The purpose of this is to manufacture a ready-to-use ethanol–hydrocarbon fuel blend. In order to demonstrate the feasibility of this proposition, we have tested an azeotropic water–ethanol feed mixture, using a hydrocarbon as entrainer, in a semi pilot-plant scale distillation column. Four different hydrocarbons (hexane, cyclohexane, isooctane, and toluene) that are representative of the hydrocarbons present in ordinary gasoline have been tested. Each of these hydrocarbons was tested separately in experiments under conditions of constant feed rate and variable reboiler heat duty. The experimentally obtained results are compared with results calculated by a simulator. Finally, the proposed and traditional ethanol dehydration processes are compared to ascertain the advantages of the former over the latter

Ethanol dehydration via azeotropic distillation with gasoline fraction mixtures as entrainers: A pilot-scale study with industrially produced bioethanol and naphta

Various hydrocarbons (n-hexane, cyclohexane, toluene, isooctane) and mixtures of them (binary, ternary or quaternary), as well as two different types of industrially produced naphtha (one obtained by direct distillation and the other from a catalytic cracking process), have been tested as candidate entrainers to dehydrate ethanol. The tests were carried out in an azeotropic distillation column on a semi pilot plant. The results show that it is possible to dehydrate bioethanol using naphtha as entrainer, obtaining as a result a fuel blend with negligible water content and ready for immediate use in motor vehicles